Determination of Organophosphate Pesticide and Nutrient Concentrations in An Agriculturally Dominated Mississippi River Tributary

Increased sediment loads in freshwater systems due to agricultural practices can have negative effects on water quality itself as well as aquatic organisms in the system. Nitrogen and phosphorus are the nutrients that generally are of great concern when found in excess in aquatic systems and the process of eutrophication is of great concern in Mississippi River basin. The Tyronza River, a tributary of the Mississippi River located in Poinsett County, Arkansas is a reservoir for many different pesticides and fertilizers used in the cultivation processes of cotton and soybeans. In this location previous data shows that nutrient loading combined with agricultural run-off and sediment loading has significantly decreased water quality and in-stream habitat. Adaptation to these conditions by freshwater mussels suggests that these organisms not only thrive in these conditions but, as data show, are functional components of the nutrient biogeochemical cycles mitigating some of the loading effects. Water and sediment samples were taken from three locations along the river: upper, middle, and lower. Samples were taken from both the surface and the sediment/water interface. Water samples were analyzed for total nitrogen, nitrate, nitrite, ammonia, total phosphorus, and orthophosphate, using a Lachat QuickChem 8000 Flow Injection Analyzer. Sediment samples were analyzed for organophosphate pesticides using Gas Chromatography-Mass Spectrometry. Water data show that nutrient concentrations are slightly higher at the surface than at the bottom. This data combined with sediment data suggest that the freshwater mussels are able to filter excess nutrients that accumulate due to increased nutrient and sediment load. We will use this data to further investigate the fate and effect of these compounds in the Tyronza River and role of freshwater mussels in the biogeochemical cycling of these chemicals.